Purpose : 5-Formyluracil (5-foU) is a major derivative of thymine produced
in DNA by ionizing radiation and various chemical oxidants. It has been pre
viously shown that 5-foU in template DNA directs misincorporation of nucleo
tides by DNA polymerases during in vitro DNA synthesis. The present experim
ents were designed to understand the biological effects of 5-foU in vivo.
Materials and methods: The modified base was incorporated site-specifically
into the recognition site of restriction endonuclease SalI (5'-GTCGAC) or
AflII (5'-CTTAAG) in vector plasmid pSVK3 and introduced the plasmid into E
scherichia coli.
Results: When the plasmids were replicated in E. coli, 5-foU caused mutatio
ns at the target sites. The induced mutation frequencies were 0.038-0.049%.
Sequence analysis revealed that 5-foU preferentially caused T:A --> C:G an
d T: A --> A:T base substitutions and -1 deletions at the 5-foU site. 5-FoU
also caused mutations at sites near the 5-foU. The alkA mutation did not a
ffect the frequency of mutations in 5-foU-containing plasmids.
Conclusions : The present experiments demonstrated that 5-formyluracil in D
NA caused mutations in E. coli.